WHY INCORPORATE SPRINTING INTO YOUR WORKOUTS
When you want to get in shape, there are four main things you need to focus on: You should eat healthy (and not overeat), do weight training, sleep enough and do your cardio.
But what exactly should you do for cardio?
Here are the 3 reasons why you should include sprints or interval training in your workouts.
1- You will lose more fat, faster!
Research has shown again and again how much more efficient sprint training is compared to steady state aerobic-training. Not only does it take WAY less time, it also makes your body burn A LOT more fat throughout the day.
In a 1994 study (yes, it's been that long that they've been proving it), participants did either 20 weeks of steady-state cardio or 15 weeks of intervals (15 sprints of 30 seconds each). The interval group lost 9 times more body fat and 12% more visceral body fat than the aerobic group!
2- Sprint training will help you build muscle
Sprinting enhances protein synthesis. If you eat enough protein in your diet, this means that will you will gain lean muscle. It also increases testosterone and decreases cortisol (the stress hormone), which makes your body more anabolic and helps you get leaner and feel better.
Interval training also targets your fast-twitch muscle fibers, which will not only help you build muscle, but also make you stronger. Instead of making you weaker like steady-state cardio, sprints will actually help you get stronger and help you lift weights.
3- Sprint training will improve your conditioning and your heart health.
If you want to improve your VO2 Max (how good and efficient your "cardio" is), the solution is intervals/sprints. Yes, they are much harder than walking for 45 minutes, but if you want to improve your conditioning, the most effective will be to sprint. This will force your body to work harder and to adjust to the higher oxygen demand from the muscles in your body. This is what will help you when you want to walk up the stairs or play with your kids.
In recent years, there has been a shift even among endurance athletes towards less volume but more quality work in their training. In other words, they've realized that running 50 kilometers won't improve their time on a marathon  as much as interval workouts will.
Since your heart has to work harder to meet the higher demands of sprints, it will adapt and this will lead to higher stroke volume (the amount of blood pumped out by your heart) and a lower resting heart rate (since your heart doesn't need to pump as often to send oxygen everywhere in your body). In other words, your body will become more efficient at sending oxygen to your muscles with sprint training, which will lead to less stress on the heart.
